A Study on Hot Tearing Behavior of Al-1 Wt Pct Cu Alloy Under Various Strain Rates During Casting Process
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INTRODUCTION
HOT tear is an internal defect generated during the solidification phase of the casting process. Such tears can seriously degrade quality of the cast product; which can lead to product’s rejection. Since hot tearing is a complex phenomenon, it is logical to find a variety of mechanisms and relevant models suggested in literature that try to explain it. Eskin and Katgerman[1] have compiled many of these models; based on their review, it has been widely accepted that the strain rate is a significant parameter in creating the necessary conditions for hot tearing to take place. Today, in practice, strain rate is considered the most important parameter effecting quality of the final product. Aluminum-copper (Al-Cu) alloys, because of their high strength and hardness at room as well as elevated temperatures, are utilized in a wide variety of applications. However, such alloys are susceptible to hot tearing.[2] For this reason, numerous studies in hot tearing phenomenon of Al-Cu alloys have been conducted in recent years. Most of these studies (which are mentioned in the followings) can be categorized into two major fields: (1) developing concepts and models that best describe the underlying mechanisms, and (2)
MAJID BAGHERI and MOSTAFA ALIZADEH are with the Department of Metals, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, PO BOX 76315-115, Kerman, Iran. Contact e-mails: [email protected], [email protected] ALI R. AHMADI is with the Department of Mechanical Engineering, Graduate University of Advanced Technology, PO BOX 76315-115, Kerman, Iran. Manuscript submitted September 3, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
development of methods and processes that would help in reducing hot tearing susceptibility (mainly through grain refinement). D’Elia et al.[3] studied the effect of grain refinement on hot tearing behavior of B206 alloy by adding titanium to the cast. They reported that adding Ti would reduce the grain size leading to a delay in dendrite coherency that improves on the liquid feeding duration. This process helps on uniformity of the strain field, which is essential for strengthening the resistance to hot tearing. Li et al.[4] conducted similar research investigating the effect of grain refinement on the hot tearing of Al-Cu (M206) alloy. They utilized Al-Ti and Al-Ti-B master alloys for the purpose of grain refinement and discovered that grain size and grain morphology effect hot tearing behavior. It was noted that the liquid film thickness between the grains was decreased because of the treatment. Based on experiments, they concluded that grain refinement improves the feeding and also leads to a more suitable distribution of stresses in the mushy zone. Zhang et al.[5] attempted to improve the hot tearing susceptibility of TiB2 reinforced Al-5Cu by adding yttrium. They found out that increasing yttrium content reduces hot tearing susceptibility. They attributed this behavior to grain refinement and shortening of the soli
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